Humans hard wired for optimism
Research in the USA and the UK has found that humans are hard wired for optimism. Research participants were found to expect that good things would happen to them sooner, often underestimating that bad things would happen.
Defensive Pessimism can be good too
On the other hand, pessimism can also be beneficial. A book on the topic of defensive pessimism, explains that anticipating that bad things can happen is not always bad. For example, someone who sees that his job is not going well at his current employer can think ahead and weigh his/her options and find another job before things turn worse. This is channelling the bad forces for a good outcome.